Abstract

Incised-valley compound fills are currently modeled in terms of multiple cycles of relative sea-level fall and rise. In contrast, the Eocene La Meseta Formation from Seymour Island is a shelf-valley geometrically compound fill, the development of which was governed mainly by local subsidence along fault-controlled valley margins and associated amplified tidal circulation. The valley contains a ≥ 330-m-thick, festoonlike stack of transgressive-regressive, marine-estuarine cycles affected by slumping and sliding, growth faulting, and warping near the margins. Aggradational stacking of the transgressive-regressive cycles reflects transgressions initiated or enhanced by episodic subsidence of the valley floor, whereas sequence boundaries record those base-level falls having rates that exceeded the rate of valley-floor subsidence. Compound fills, particularly those of shelf-valley systems developed along active basement structures, should not necessarily be attributable to regional base-level changes alone.

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